Whether hydraulic or pneumatic knee joint is a passive prosthesis, walking is realized by the leg swing driven by the thigh stump. According to the changes of external conditions, the knee joint damping moment of the thigh prosthesis can be adjusted to achieve gait adjustment. Because the control mode is relatively simple, the difficulty of implementation is relatively small, and the energy consumption is relatively low, it has been widely used. The intelligent thigh prosthesis belongs to the active prosthesis, which mainly uses the motor as the power source, and can provide the torque instead of the leg muscles, so that the knee joint can be bent and extended actively.

According to the structure, knee prosthesis can be divided into single axis prosthesis and multi link prosthesis. The single axis knee joint has only a single rotation axis, so it has high flexibility in the swing period, but it is not stable in the support period. Most of the multi axis knee joints are multi link knee joints (four, five or six). The design of multi link mechanism enables the rotation center to move in a certain trajectory, which is more in line with the change of the knee joint rotation center during normal walking of human body. The rotation instantaneous center can be larger than the rotation axis during stretching, and it can quickly descend to the vicinity of the rotation axis during bending, so that it can stretch flexibly and support at the same time It's also stable. The single axis pneumatic knee joint is suitable for the patients with long stumps. It is characterized by the flexibility of the joint body, and the disadvantage is that it is not easy to control. The air pressure knee joint with four-bar linkage has many suitable types of residual limbs, and its characteristics are relatively stable.

Air pressure knee joint: high flexibility, small motion damping, low requirement for force, gentle and gentle swing, low requirement for temperature (basically not affected by temperature), light weight of gas. Disadvantages: because the air compression rate is slightly larger (in place) and the accuracy is slightly worse than the hydraulic pressure (but people's weight is generally within 150 kg, so the compression rate is very small, so the impact is not significant).

At present, the multi axis pneumatic knee joint is more loved by the prosthetic patients. Compared with the single axis pneumatic joint, the multi axis joint is better in safety, more stable in practical performance, and more beautiful in walking gait. For example, Ottobock's 3r78 "yuebu" four-bar structure ensures that the patient can walk stably and naturally. The design of yuebu is small and light, with a weight of only 750g, which is far lighter than similar products, greatly saving patients' physical strength. With the change of knee flexion damping design, the patient can walk closer to the natural gait and travel safely. Flexible knee bending and stretching, optimized cylinder control system, make the swing period more meet the daily walking speed and comfortable walking needs: catch the bus, cross the road, rainy days, etc., so that users can go further. The natural and harmonious appearance also meets the aesthetic needs of patients.